Copolyesters of poly(hydroxyalkanoates) with aromatic dicarboxylic acids are known within the art. For example, Gordon, et al., in WO 91/02015, disclose hydrodegradable aliphatic-aromatic copolyesters that can include hydroxy acids. Imamura, et al., in U.S. Pat. No. 5,605,981 and U.S. Pat. No. 5,616,657, disclose a process for the preparation of certain lactic acid copolyesters comprising 98–50 weight percent lactide. Warzelhan, et al., in U.S. Pat. No. 5,817,721 U.S. Pat. No. 6,018,004 and U.S. Pat. No. 6,303,677 and U.S. Pat. No. 5,889,135, disclose certain aliphatic-aromatic copolyesters containing hydroxy acid components. Buchanan, et al., in U.S. Pat. No. 6,342,304, disclose oriented films derived from linear aliphatic-aromatic copolyesters prepared from polyester forming combinations of hydroxy acids, dicarboxylic acids or derivatives thereof, and diols.
Copolyesters of poly(hydroxyalkanoates) with aromatic dicarboxylic acids and also containing a sulfonate functionality are also known. For example, Gallagher, et al., in U.S. Pat. No. 5,097,004, U.S. Pat. No. 5,171,308, and U.S. Pat. No. 5,219,646, Tietz, in U.S. Pat. No. 5,097,005, and Romesser, et al., in U.S. Pat. No. 5,295,985 disclose certain sulfonated aromatic copolyesters that contain 2 to 40 weight percent of a hydroxy acid component. Warzelhan, et al., in U.S. Pat. No. 6,018,004 and U.S. Pat. No. 6,303,677, disclose sulfonated aliphatic-aromatic copolyesters that contain hydroxy acids.
Known aromatic copolyetheresters having hydroxyalkanoic acid components can have inadequate thermal properties for some applications, as evidenced by the low observed crystalline melting temperatures and glass transition temperatures. The present invention provides aromatic copolyetheresters made from hydroxyalkanoic acids, having improved thermal properties, such as crystalline melting points, glass transition temperatures, and heat deflection temperatures, in comparison with known aromatic copolyetheresters made from hydroxyalkanoic acids.